1. Field of the Invention
The present invention relates to a driving electrolyte and an electrolytic capacitor using the same.
2. Description of the Related Art
Nonaqueous driving electrolytes containing an organic carboxylic acid such as azelaic acid, sebacic acid, adipic acid, or the like, or the salt thereof as the solute in ethylene glycol as the solvent have been known as the driving electrolytes conventionally used for electrolytic capacitors. These nonaqueous driving electrolytes have long been used for high-voltage applications, as they are relatively favorable in chemical self-restoring ability even under an environment at 100° C. or more. Here, the chemical self-restoring ability means an ability to repair the defects on dielectric oxide films when formed.
Because the nonaqueous driving electrolytes above degrade more readily due to esterification reactions that occur at high temperature, a dibasic acid having one or more side-chains such as 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, or the like, or the salt thereof has been commonly used therein as the electrolyte for suppressing the esterification reactions. Such electrolytic capacitors include, for example, the electrolytic capacitors disclosed in Jpn. Unexamined Patent Publication Nos. 2-224217 and 3-209810.
On the other hand, for electrolytic capacitors for use in harmonic-suppressing circuits and vehicle applications, there exists more recently a demand for a driving electrolyte that is higher in electrical conductivity, higher in sparkover voltage at high temperature, longer in lifetime, more resistant to breakdown of the dielectric oxide film on electrodes, and superior in the ability to repair defects on the dielectric oxide film when formed (chemical self-restoring ability) and to suppress chemical reactions at high temperature.
However, when a dibasic acid having a side-chain or the salt thereof described above is used as a solute of driving electrolytes, the dibasic acid having a side-chain or the salts thereof, such as containing only a side chain in the neighborhood of only one of the carboxyl groups, do not have sufficiently high heat resistance at elevated temperature and leads to significant decrease in electrical conductivity at high temperature due to easier esterification reactions of the carboxyl groups of solutes with alcohols such as ethylene glycol and the like therein over time and consequently to significant deterioration in the properties of electrolytic capacitors.